1. Field of the Invention
The present invention relates to a heat exchanger, more particularly a heat exchanger which can maintain a certain range of temperatures of a fluid at an outlet port of the heat exchanger.
2. Description of the Prior Art
In a conventional heat exchanger for exhaust heat recovery, a bypass passage for exhaust gas is separately provided from the heat exchanger in order to maintain a slightly higher temperature than the condensing temperature at an output port of the heat exchanger and also effectively perform heat recovery. Moreover, a temperature sensor provided at the output portion, signal transmitting means for transmitting a signal, and a changing valve located at an inlet port of the heat exchanger for controlling the exhaust gas at the inlet port according to the signal from signal transmitting means are provided for attaining the abovementioned function. Accordingly, the exhaust gas at the inlet portion of the heat exchanger is selectively supplied to the outlet port through the heat exchanger or through the bypass passage according to the temperature at the outlet port.
In the case where the exhaust gas is supplied to the outlet port through the bypass passage, heat recovery is not performed. As above mentioned, the bypass passage, the temperature sensor, the signal transmitting means, and the changing valve are quite necessary, so that the entire construction of the heat exchanger becomes complicated and the number of parts necessary is also increased.